[fprint] elan patch + poc 0x903 and 0x0C03

[Igor Filatov]

Hi Timo,

I've noticed this when working on the initial implementation - that rows at
bottom and top are bad (and I've seen a number of scans sent by different
people - it's never on the sides for some reason). That's why there was the
frame_margin param which means "cut this many px from top and bottom".
Actually, in recent commits this has changed and it just crops the frame to
max 50px by height. Since assembly doesn't really work for frames higher
than that.

But ultimately libfprint needs a different algo for small sensors. No
getting around it. Telling people they need to swipe even though they see
have a touch sensor isn't feasible and seems to already be failing in
practice. I've trained myself to swipe reliably but still... don't want to
spoil my karma with a driver that pretends to work but is hardly usable.



> Hi,
>>
>>
>>
>>
>>
>> I might actually have another solution.
>>
>> The fingerprint images, that are created by the swiping, are assembled
>> out of multiple images, the reader got, right?
>> I now realized that each of those images seems to have about one or two
>> rows of pixels at the top and at the bottom, which are simply black.
>> Those rows alter the image, so that similar fingers aren’t matching, as
>> the rows are at different positions in the image if the finger was moved
>> with a different speed – which is always the case.
>> So I think we should try changing the way we generate the image with the
>> swipe movement by cropping each image, of which the final image is
>> assembled, by two pixels at the top and the bottom.
>> I don’t know whether this solves all problems, but I can at imagine that
>> it’d at least improve it.
>> I am however still working on an alternative algorithm, which uses cross
>> correlation of field orientation, but I can imagine that this won’t be
>> necessary anymore.
>>
>>
>>
>> I don’t know the way you’re currently assembling the joined fingerprint
>> image, so maybe someone who does could give this a try?
>> I’ll be happy to test it afterwards.
>>
>>
>>
>>
>>
>> Kind regards
>>
>>
>>
>> Timo
>>
>>
>>
>> *From:* fprint [mailto:fprint-bounces at lists.freedesktop.org] *On Behalf
>> Of *wp12880529-timo wp12880529-timo
>> *Sent:* Friday, 9 February 2018 03:30
>> *To:* Hans de Goede <hdegoede at redhat.com>; Sebastien Bechet <
>> sebastien.bechet at osinix.com>; Igor Filatov <ia.filatov at gmail.com>
>> *Cc:* fprint at lists.freedesktop.org
>>
>>
>> *Subject:* Re: [fprint] elan patch + poc 0x903 and 0x0C03
>>
>>
>>
>> Hi Igor,
>>
>>
>>
>> I tried the new version, which doesn't seem to work significantly better
>> - it detects about 50% of the tries. I think the best solution will be
>> another algorithm, which I'm currently working on.
>>
>>
>>
>> Kind regards
>>
>>
>>
>> Timo
>>
>> Igor Filatov <ia.filatov at gmail.com> hat am 4. Februar 2018 um 16:07
>> geschrieben:
>>
>> Hi everybody,
>>
>>
>>
>> Base on the new info I got I've updated the driver in a few places:
>>
>>
>>
>> 1. Frames are cropped to 30px by height. I've received some examples of
>> images from 96px readers and it seems that the assembling procedure just
>> doesn't work for frames of greater height. I _think_ this is largely
>> because the skin stretches and deforms in a non-uniform way when you swipe.
>> E.g. the same part of the print is slightly different when it's near the
>> bottom of the frame than when it's near the top. Plus, there often seem to
>> be sensor artifacts near the edges, so.
>>
>>
>>
>> 2. Sensor reset is out. Devices do it when they power up. I'm not
>> entirely sure that it's absolutely not needed, though. I'm thinking about
>> suspend & resume, for one. But anyway, I've used my reader for long without
>> any reset and I'm suspending all the time and I haven't had any problems
>> because of it.
>>
>>
>>
>> 3. Some changes around calibration. You can get a calibration status of
>> 0x01 (ongoing) and 0x03 (completed) from the device. But I've noticed that
>> very often the first response I get is 0x03, which later (~100 ms) changes
>> to 0x01, then back to 0x03. So now to make sure it actually completes, the
>> driver first wants to see 0x01 at least once and then it waits for 0x03.
>>
>>
>>
>> 4. KT has recommended a different frame extraction algo. First we
>> subtract the background which we got during calibration. This helps quite
>> significantly. Then we split values into 3 groups and apply a different
>> transformation to each group (see comments for detail). And this seems to
>> give slightly worse results on my reader than simple linear scaling like
>> there was before. So I've left both methods and it's possible to configure
>> the method for each device. YMMV.
>>
>>
>>
>> Please see if it now works better/same/worse for you. I think
>> verification is now slightly better on my device but I need to use it for a
>> couple of days to know.
>>
>>
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/fprint/attachments/20180209/f5a6c355/attachment.html>